Generally, gas turbine engines operate by burning fuel and extracting energy from the combusted fuel to generate power. Atmospheric air is drawn into the engine from the environment, where it is compressed in multiple stages to significantly higher pressures operating at higher temperatures. The compression is accomplished in the compressor section of the engine. An optional fan section may be located before or in front of the compressor section, that is, fore of the compressor section in certain engines. In addition, the fan section may have multiple stages. A portion of the compressed air is then mixed with fuel and ignited in the combustor to produce high energy combustion gases. The high energy combustion gases then flow through the turbine section of the engine, which includes a plurality of turbine stages, each stage comprising turbine vanes and turbine blades mounted on a rotor. The high energy combustion gases create a harsh environment, causing oxidation, erosion and corrosion of downstream hardware. The turbine blades extract energy from the high energy combustion gases and turn the turbine shaft on which the rotor is mounted. The turbine shaft rotation also results in rotation of the compressor section and the fan section, which sections may be directly mounted on the turbine shaft, or more likely, connected to the turbine shaft with gearing and/or auxiliary shafts. The turbine section also may directly generate electricity. A portion of the compressed air is also used to cool components of the turbine engine downstream of the compressor, such as combustor components, turbine components and exhaust components.
Aircraft gas turbine engines are a subclass of gas turbine engines. These engines generally are operated using jet fuel. Furthermore, the exhaust gases passing through the turbine section are used to propel the aircraft. In addition, one of the long sought after goals for aircraft gas turbines is improved operating efficiency, which can be accomplished by weight reduction of the aircraft engine itself and by increasing the temperature capabilities of the turbine itself, so that additional energy can be extracted from the combustion process.
Weight reductions in aircraft turbine engines are a source of improved operating efficiencies. One area of improved operating efficiency is the use of lighter weight materials in the engine, in particular, regions aft of the hot section of the engine. These areas have posed not only the greatest opportunities but also the greatest challenges. Such opportunities are available in the hot section of the engine because the hot section of the engine substantially comprises metals, such as superalloys, that tend to have a high density as compared to non-metallic materials. The hot section components aft of the compressor furthermore can be relatively large and therefore relatively heavy. However, superalloys are utilized for these hot section components because they provide the unique combination of mechanical properties at high temperatures as well as corrosion resistance, oxidation resistance and erosion resistance.
Any reduction in weight resulting from substitution of lighter weight material for metallic hot section components is desirable. However, the substitution of materials in a hot section engine component must not adversely affect the engineering performance of the hot section component. The component must at least maintain its mechanical properties at high temperatures while also providing corrosion resistance, oxidation resistance and erosion resistance.